This invention relates to temperature and/or humidity conditioning systems generally, and more particularly to heating, air conditioning and ventilating systems and, with even more particularity, to systems having variable speed operation which is responsive to a two state temperature signal as provided, for example, by a thermostat.
Variable capacity central heating, ventilating and air conditioning (HVAC) systems are typically controlled by electronic thermostats containing microprocessors which continuously monitor indoor air temperature by a thermistor or other means. The thermostat temperature set point is compared to the sensed or monitored temperature value and the microprocessor in the thermostat evaluates this differential to generate a control signal. It should be apparent that it would be desirable to provide a system which eliminates the need for a microprocessor within a thermostat or as part of a system controller. It would also be desirable that such an improved system (or parts thereof) be generally useable for controlling the humidity or temperature of air generally.
Some HVAC systems have utilized sequencing of the outdoor fan motor, compressor, and indoor blower to maximize efficiency on start up and shut down (See, for example, U.S. Pat. No. 4,941,325). Alternatively, some systems delay operation of various components in an effort to improve air delivery temperature (See, for example, U.S. Pat. No. 4,860,552). However, these systems do not respond to environment changes and cannot be programmed to permit variable sequencing or delays depending on the temperature signal generated by a conventional thermostat.
Further, present system applications require that the starting torque and/or speed-torque characteristics of the motors be predictable and repeatable. In addition, it is desirable that motors be operable at the highest reasonably achievable efficiency consistent with mass production techniques. Known present variable speed motors cannot easily achieve this advantage because it has traditionally been impractical or too costly to minimize the variable effect on motor characteristics caused by manufacturing tolerances of the internal components of the motor. Present concepts and arrangements for adjusting a motor for different applications require circuit changes such as multiple variable resistors in the electronic control for the motor or permanent software changes in an electronic control microprocessor. Both of the aforementioned arrangements are disadvantageous because they require a unique model to be built for calibrating a system which cannot be easily changed and can be quite expensive.